Many types of seat apparatuses each having a load detecting device for detecting a load of an occupant seated on a seat have been proposed to be applicable for vehicles mounted with airbags adapted to protect occupants. An output of the load detecting device is employed so as to appropriately adjust an amount of gas emissions of an air bag to be inflated, corresponding to a weight of an occupant. Further, when an occupant seated on a seat is determined to be a child based upon an output of the load detecting device, a pin of the air bag is controlled not to be operated.
For example, JP2006-38812A (Reference 1) discloses therein an occupant weight measurement device for a vehicle seat, in which multiple load sensors for measuring a weight of an occupant are arranged between a frame supporting a seat cushion and a pair of upper rails mounted on a pair of lower rails fixed to a floor of a vehicle to be movable in a longitudinal direction.
As illustrated in FIG. 4 of Reference 1, the load sensor includes a cylindrical sensing portion (52) having a strain gauge detecting a load; a plate-shaped flange (51) extending at a lower end of the sensing portion (52) forward and rearward in a horizontal manner; a load input rod (53) extending upwardly from an upper end of the sensing portion (52); and a connector (54) extending from the sensing portion (52) to be in parallel with the flange (51). The flange is fixed to the upper rail and the load input rod (53) is fixed to the frame supporting the seat cushion. So configured, when an occupant is seated on the seat cushion, a weight of the occupant is applied to the load sensor via the frame, and the load sensor detects the weight of the occupant as an electrical signal.
In the above-described occupant weight measurement device disclosed in Reference 1, a vertical dimension (height) of the load sensor positioned between the upper rail and the frame supporting the seat cushion may be increased, so that a distance between the upper rail and the frame may become large. That is, a large space is required between the upper rail and the frame, which large space is used to accommodate the cylindrical sensing portion and the connector of the load sensor.
Reference 1 does not disclose therein the method for processing an electrical signal transmitted from the connector. However, in general, this type of occupant weight measurement device requires an amplifier unit for amplifying an electrical signal detected by the strain gauge. In this case, according to the structure of the load sensor disclosed in Reference 1, an amplifier unit needs to be provided separately at another position, which is connected to the connector via a communication line. Therefore, an output of the load sensor is not amplified in the vicinity of the load sensor.
A need thus exists for a seat apparatus for a vehicle having a load detecting device for measuring a load of an occupant seated on a seat for a vehicle, which is not susceptible to the drawback mentioned above.